The main focus of this paper is on the extent to which radiological expertise is based on low-level perceptual processes. Experiment 1 showed that naive observers can perform well above chance level in classifying mammograms with just a few hours training. Experiment 2 showed that expert radiologists performed better than naive observers on a 'perceptual simulation' of a radiographic task, even though high-level knowledge of anatomy and disease processes was of no assistance. Experiment 3 showed that one of the fundamental parameters of the visual system likely to be involved in radiographic performance- contrast sensitivity-could be improved with practice. Experiment 4 showed that naive observers improved on a similar perceptual simulation task as used in experiment 2, and that although there was partial interocular transfer, the results suggest that at least some degree of learning was based on low-level perceptual processes. Overall the results show that some degree of skill in radiological search can be acquired with no high-level medical knowledge at all, and that some aspect of radiological skill may be based on changes in the effectiveness of early visual processes.